[Help needed] How to clean and repair this brick retaining wall

[earnest]

Could you please help with the brick wall issues? Any help and advice are appreciated.

The plan I have in mind is to do the following:

1. Power wash it first, will try to use medium level pressure
2. To use a hydrochloric acid based cleaning solution (HCl, 15-20%)
3. Replace cracked bricks
4. Repoint the rest

I have never done any brick work, so will be doing research on those topics. So please do share useful videos and articles or general advice.

A few questions regarding the brick problems, please:

1. Why would certain bricks crack that badly?
2. Why is it coming apart like a layered cake?
3. What would be the best way to work on that large gap where the walls are holding together?

 

[Jameshow]

Sounds good

5 seal bricks with brick sealer - this will stop water entering the bricks and causing cracking when the water freezes . .

 

[earnest]

Sounds good

5 seal bricks with brick sealer - this will stop water entering the bricks and causing cracking when the water freezes . .

At the top or everywhere ?

 

[niall Y]

You can often reuse damaged bricks by flipping them. around and using the internal faces on the outside. Whether you can get the bricks out neatly depends on the mortar used. Sand and cement you're going to struggle but lime should be easy.

 

[Cabinetman]

Just read the other day that a lot of that spalling is the result of soft bricks and people repointing with the wrong mortar, should be lime mortar on those old hand made bricks, I took this picture the other day as it shows the folding of the clay within the brick as it was thrown into the box.
Ian

 

[earnest]

Just read the other day that a lot of that spalling is the result of soft bricks and people repointing with the wrong mortar, should be lime mortar on those old hand made bricks, I took this picture the other day as it shows the folding of the clay within the brick as it was thrown into the box.
Ian
View attachment 182185

Thanks. How can I tell if my bricks are hand made? They look pretty much uniformly the same

 

[Cabinetman]

To be perfectly honest, I’m sorry I don’t know. I think you need to look at the mortar, if it’s the old Lime type you should stick with the same.

 

[TomGW]

The issue is caused by the bricks absorbing water and then freezing (expanding) and 'blowing' the face off - known as spalling.
The top, capping, row of bricks will be the worst affected, as that's the most exposed to absorbing rainwater. However, in a retaining situation the whole wall will have a reduced opportunity to dry at any time.
Bricks are rated for their suitability for various climate and exposure conditions and these were not best suited for this job. At the very least, the capping row should be 'engineering' brick or one approaching that grade - that will be smooth faced and very dense. A concrete coping with a drip channel would be more practical but I agree that a brick capping looks better.
In your situation I would replace the entire brick capping with a similar coloured engineering brick. Then, where the wall is retaining, provide drainage holes to reduce water build up behind and, where the wall isn't retaining seal the brickwork on both sides.
BTW, they are not hand made brick - they are metric sized and, at a guess roughly max 40 years old.

 

[earnest]

@TomGW, thanks. Would reclaimed bricks be good for replacing the severely damaged ones?

 

[TomGW]

@TomGW, thanks. Would reclaimed bricks be good for replacing the severely damaged ones?

Reclaimed bricks would be good providing you can get a good match. Also it may be easier to buy a small number. Otherwise you should see if you can get new bricks to match. Your bricks shouldn't be too hard to match with new from current ranges. Go to your local builders provider and pick up brochures of what they can supply.
For example, this would be my first guess:

https://www.forterra.co.uk/product/claydon-red-multi-london-brick/



I would highly recommend replacing the capping course with new engineering brick, either red to match or blue/black for contrast. From your photos it would appear the worst of the damage is at the bottom of a curved section where the maximum water would have pooled and soaked in. If you do that you may salvage a few sound bricks that could be used to replace other damaged bricks within the wall.

Read the links below for a bit of clarification. It won't solve the problem but it will help you understand what you're dealing with.

https://www.wienerberger.co.uk/content/dam/wienerberger/united-kingdom/marketing/documents-magazines/technical/brick-technical-guidance-sheets/UK_MKT_DOC_Durability of Clay Brickwork (REV2).pdf

https://www.modularclayproducts.co.uk/news/brick-durability-ratings/

 

[Jake]

Those are not particularly old bricks, they look a bit like flettons to my non-expert eye (if so, cheap and not very durable).

The 'large gap' is a movement joint. When new they are sealed up with a high modulus (flexible) sealant on the surface of the joint over a foam sheet between the two ends of the walls (with metal movement ties restraining the movement between the two sections of wall). The sealant needs to be replaced. Many makes but (having just bought some) Everbuild 825 has a lot of colours to match the brickwork. If you can't detect any foam sheet inside the joint, buy some foam joint rod to push into the joint, the depth of the sealant is better quite shallow than trying to fill too much of the joint up and unless you have something inside to push the sealant up against you won't achieve that.

 

[earnest]

Reclaimed bricks would be good providing you can get a good match. Also it may be easier to buy a small number. Otherwise you should see if you can get new bricks to match. Your bricks shouldn't be too hard to match with new from current ranges. Go to your local builders provider and pick up brochures of what they can supply.
For example, this would be my first guess:

https://www.forterra.co.uk/product/claydon-red-multi-london-brick/



I would highly recommend replacing the capping course with new engineering brick, either red to match or blue/black for contrast. From your photos it would appear the worst of the damage is at the bottom of a curved section where the maximum water would have pooled and soaked in. If you do that you may salvage a few sound bricks that could be used to replace other damaged bricks within the wall.

Read the links below for a bit of clarification. It won't solve the problem but it will help you understand what you're dealing with.

https://www.wienerberger.co.uk/content/dam/wienerberger/united-kingdom/marketing/documents-magazines/technical/brick-technical-guidance-sheets/UK_MKT_DOC_Durability of Clay Brickwork (REV2).pdf

https://www.modularclayproducts.co.uk/news/brick-durability-ratings/

Thanks, I was also advised to use 5:1 or even 6:1 sand and cement mixture for the mortar.

 

[Jake]

I don't think the problem is the mortar strength, the face bricks aren't spalling around the mortar joints, it looks like just the brick on edge coping which is going to be freeze-thaw on bricks which are too pervious to water to be suited to the task.

Those are definitely not old bricks and not handmade. I just showed those pics to my bricklayer who is doing a garden wall for me and he immediately said those are flettons.

Retaining walls are all 'under DPC' so a strong mix is recommended (usually 3 to 1 I think).

The best solution is probably just to remove the bricks on edge and replace that course with engineering or F2 bricks.

 

[earnest]

I don't think the problem is the mortar strength, the face bricks aren't spalling around the mortar joints, it looks like just the brick on edge coping which is going to be freeze-thaw on bricks which are too pervious to water to be suited to the task.

Those are definitely not old bricks and not handmade. I just showed those pics to my bricklayer who is doing a garden wall for me and he immediately said those are flettons.

Retaining walls are all 'under DPC' so a strong mix is recommended (usually 3 to 1 I think).

The best solution is probably just to remove the bricks on edge and replace that course with engineering or F2 bricks.

how screwed am I because these bricks are used in the fence and retaining walls? Also, they are probably used in the house too.

The 5:1 mix ratio was more when I come to repair and repoint them, thanks.

 

[thetyreman]

I'd repoint with 1:2:9 cement lime sand mix, and avoid builders sand, you want washed sharp sand. making a cement/lime hybrid mix is no harder than a cement sand mix, you don't need a mixer, just use a metal bucket, if you get calibux cl90 you can mix it hot and slake the lime, the cement acts as a pozzolan, and means it'll set much faster.

 

[thetyreman]

3:1 is also way too strong! likely what has caused the spalling in the first place, 6:1 would be much better, if you must use cement.

 

[Jake]

how screwed am I because these bricks are used in the fence and retaining walls? Also, they are probably used in the house too.

The 5:1 mix ratio was more when I come to repair and repoint them, thanks.

The bricks will be fine elsewhere, it is just that they are too porous to be used as coping where all the water hits it and sits on it etc. They are good strong bricks, just on the cheaper side because the appearance is all an applied layer to the outside of an orange brick.

 

[Jake]

3:1 is also way too strong! likely what has caused the spalling in the first place, 6:1 would be much better, if you must use cement.

Who knows what mix was used, but that's the recommended below DPC sand/cement mix these days (and retaining walls are below DPC by definition on the retaining bit).

 

[Jake]

I'd repoint with 1:2:9 cement lime sand mix, and avoid builders sand, you want washed sharp sand. making a cement/lime hybrid mix is no harder than a cement sand mix, you don't need a mixer, just use a metal bucket, if you get calibux cl90 you can mix it hot and slake the lime, the cement acts as a pozzolan, and means it'll set much faster.

Cement/lime mixes with more lime than cement are deprecated these days because apparently they micro-crack. 2:1:9 or 2:2:9 or 1:1:6 are said to be much better. I've just used 2:1:9 for for a very minorly retaining wall to try to match my house's lime pointing but needed to lay in Nov/Dec temps. It works, they all work, only time will tell how well.

I think this will be fine anyway with whatever mix as it's just some pointing (although the coping is going to get a hard time of it, as the bricks are saying). However a mix with lime in it will come up much lighter than the existing pointing, so that would look a mess unless he repoints the whole wall (despite that not looking necessary for the most part).

Whatever he does with mortar, those bricks are not up to the role of being copings so a long term fix would replace those, a decent brickie will be able to match the existing mortar well enough to patch point it where that is needed.

 

[thetyreman]

Cement/lime mixes with more lime than cement are deprecated these days because apparently they micro-crack.

can you show me some evidence for this? from my experience it's actually cement that causes cracking and builders sand, the 3:1 mix you recommended is way too hard and won't fix the issue, look up liquid phase egress from cement pointing, in short cement is too hard for these bricks, and water can't evaporate out of the mortar so it tries to get out of the brick instead, that's why the surface has fallen off, I see it everywhere especially on garden walls, very common to see dave the local builder putting a 3:1 mix over a hot lime mortar thinking they've 'fixed' the problem when they're just making it 10x worse and potentially causing tens of thousands pounds worth of damage whilst happily taking the cash from unsuspecting home owners.